The present invention relates to support rolls for underfloor turning machines for the remachining of worn wheel profiles of a wheel set in a continuous operation, in which each wheel of the wheel set is supported by two support rolls which are arranged spaced from each other substantially in a plane normal to the axis of the wheel set.
Such underfloor turning machines for wheel sets are known in the art and for instance disclosed in the German Pat. Nos. 1,043,020 and 1,082,478. In these known machines, each wheel of the wheel set is driven by two friction rolls engaging the tread surface of the respective wheel. The cutting operation during the reprofiling of the wheel profiles in these known machines has to be interrupted and the friction rolls have to be transposed as clearly explained in the German Pat. No. 1,082,478. This known method is therefore time consuming and difficult to carry out. Attempts have therefore been made to further develop such machines for reprofiling wheel sets in a continuous operation, that is without interrupting the cutting operation during reprofiling and while the wheel sets remain on the vehicle.
To obtain this desired result, an underfloor turning machine has already been disclosed in the DT-AS 1,477,697, in which each wheel of a wheel set is alternatingly supported by a tread surface roll pair and a rim surface roll pair. This known turning machine is however extremely complicated and the results obtained therefrom are far from perfect. The transfer from one to the other roll pairs cannot be carried out without undue shocks so that corresponding marks will be produced on the tread surface of the wheel. This known machine requires further additional friction drive rolls which engage the wheels at the end faces thereof. This entails not only a complicated construction, but has the additional disadvantage that the drive rolls are subjected to considerable friction and corresponding wear so that they will not stand up after extended use. Furthermore, the support carrying the turning tool has to be arranged in the last mentioned machine in a position as shown in FIG. 2 of the DT-AS 1,477,697. This arrangement of the turning tool has, however, proven disadvantageous. In order to obtain satisfactorily out of round of the wheels of the wheel set, the turning tool should be arranged between the two drive rolls. Such an arrangement is, however, impossible in the last-mentioned machine.
The journal "Revue Generale des Chemins de Fer", May 1960, pages 271-279 discloses and describes further an underfloor turning machine in which each wheel of a railroad wheel set is driven by a pair of friction rolls. With this machine it is possible to turn the wheel profile in a continuous operation. Each drive roll (see page 276, FIG. 9) is relatively narrow and has an at least substantially cylindrical carrying zone and to opposite sides of the latter about 45.degree. inclined discharge or transfer zones, through which a transfer from the not yet machined worn wheel profile to the new properly machined profile is made possible. In this known machine, each drive roll has, as viewed in axial direction of the wheel set the same position as would be taken by a rail during movement of the wheel set in longitudinal direction on a straight rail. In this known machine, the wheel set to be machined is positively supported by special means and the drive rolls are moved non-positively against the wheel set to turn the wheels. At the beginning of the machining operation, only the carrying zone of the drive roll profile is in contact with the worn profile of the wheel. The tool increasingly cuts the carrying zone clear until finally the cut edge of the wheel, resulting from the machining, will engage the transfer zone and move downwards along the same due to the continuing machining until the profiled portion, machined at the beginning, will engage the carrying zone. From this moment until the end of the machining operation, the wheel is in engagement only with the carrying zone.
In this construction the relatively great inclination of the transfer zone with respect to a horizontal plane is especially disadvantageous. Due to this inclination, there will result a considerable force component of the respective wheel set load portion directed toward the center plane of the machine and parallel to the wheel set axis, which acts on the effective radius of the wheel as lever arm, resulting in a bending of the wheel set shaft and corresponding inclined position of the wheels. The individual wheel will be thereby machined during the transfer period in an inclined position so that after resilient relaxation of the wheel set, at the end of the machining operation, a distorted tread profile will result. It is a further disadvantage that, during the change from the carrying zone to the greatly inclined transfer zone and the subsequent retransfer onto the carrying zone, a continuous change of the position of the wheel, due to the changing bend of the wheel set shaft, will result, which in turn will entail further defects in the desired machined profile.
From the journal "French Railway Techniques", No. 2, April-May-June 1961, and the article "New Development on the Re-profiling of Wheels without Dismounting Wheel Sets", Section IIIA, there is known a friction wheel pair, whereby the profile of each friction roll corresponds to the standard rail profile.
During transfer of tangential forces by friction there will necessarily result a slippage between the driven and the driving element. A predetermined slippage will therefore result from any predetermined tangential force. If the magnitude of the slippage surpasses or falls short of an optimum slip magnitude, the transferrable tangential force is reduced (see in this respect: "Der Kraftschluss zwischen Rad und Schiene" von Dr.-Ing. Arnold Tross, Munich, Glasers Annalen 93 (1969), Nr. 10 Oktober, S. 310-320, as well as "Wirkungsgrade der Vortriebstechniken spurgefuhrter Fahrzeuge" von Dr.-Ing. Ekkehard Gartner (KDT), Hennigsdorf, DET-Die Eisenbahntechnik 23 (1975), Nr. 1, Seite 18 bis 20).
A slippage diagram is known from a great number of tests from the two last-mentioned publications, which in principle has an outline as illustrated in the corresponding slippage diagram in FIG. 10 of the present application. In this diagram the slippage S is shown on the abscissa and the friction coefficient .mu. is shown on the ordinate. The resulting curve shows a reversal point which indicates the highest possible transfer of a tangential force. This diagram shows clearly that an optional slippage of predetermined size will result in the highest obtainable transfer of tangential force. It the slippage surpasses or falls short of the optimal slippage, then the transferrable tangential force is reduced, that is, the two frictional engaging elements behave as if the initially provided friction coefficient .mu. would not be reached. The capability of the two elements which are in frictional rolling engagement with each other to transfer tangential forces is therefore continuously reduced with increasing deviation from the optimal slippage. The greatest tangential force can be transmitted between two bodies, in rolling engagement with each other and having parallel axes of rotation, when both bodies are of cylindrical form. With increasing conicity of the two rotational bodies which are in rolling engagement with each other, the maximum transferrable tangential force is increasingly reduced, under otherwise identical conditions.
Due to the relatively large inclination of the transfer zone of the friction drive roll of the below-the-floor turning machine described in the journal "Revue Generale des Chemins de Fer", the transferrable tangential force is therefore reduced. Due to the large inclination of the transfer zone, the respective wheel set load portion, that is the force at which the rollers are pressed against the wheels must therefore be held relatively small in order to reduce the forces acting parallel to the axis of the wheel set, which will bend the wheel set shaft, and which thereby will result in an inclined position of the wheels of the wheel set. Due to the reduced force with which the drive rolls are pressed against the wheels of the wheel set, only a transfer of relatively small tangential forces is possible, the size of which is, however, decisive for the machining efficiency and therewith for the output of such a machine.